Electrical alternators adapted for use in motor vehicle applications typically include a rotor assembly rotatable within an annular stator. Rotor pole pieces, which may preferably be of an interleaved “claw pole” design, rotate with the rotor shaft, while the stator itself includes a stator core defining radially-extending slots in which a plurality of stator windings are disposed. An excitation winding is carried within the cavity formed between pole pieces of the rotor, and a DC signal is applied to the excitation winding through a pair of slip rings and associated brushes. The magnetic field produced by the winding interacts with the pole pieces to create an alternating polarity magnetic field which, upon rotation of the rotor assembly as driven by the vehicle's engine, induces current flow in the stator windings in a known manner.
Because the resistance of the conductors of the stator windings is inversely proportional to alternator output and efficiency, cooling of the stator winding is an important factor for improving alternator output and efficiency. To achieve higher electrical outputs while reducing the overall size of the stator, the prior art has, therefore, sought to employ stator conductors of square or rectangular cross-section to enhance conductor surface area and, hence, enhance convective cooling of the stator windings. Such wire can be laced into the stator core winding slots in a very densely packed configuration, thereby improving “slot space utilization.” However, square- or rectangular-cross-section wire is more difficult to form and wind into the stator winding slots, since it is necessary to align the conductor cross-section with the slot.
Designers of stator assemblies further attempt to reduce or eliminate the need for providing electrical conductor terminations and connections in the stator assembly, as a need to physically connect conductors in the stator core assembly adversely impacts cost and complexity of the manufacturing process. To this end, stator windings utilizing continuous conductors with which to form each phase have emerged, including those having a square or rectangular cross-section for use in high-slot-fill, multi-phase stator winding configurations. Each such continuous conductor includes a series of straight segments, disposed in respective slots of the stator core, which are interconnected by end loop segments that project axially from either end of the core. The end loop segments are readily formed of first and second legs that extend first radially-outwardly and then radially-inwardly, respectively, to thereby permit successive straight segments to reside in a common layer, thereby providing a desired cascaded winding configuration.
Such windings typically feature an interleaved radial transition of each conductor between layers, i.e., at the end of a complete revolution, the conductors of the different phases trade radial positions within the stator winding with respect to each other. Such transitions present significant manufacturing challenges and costs, for example, often requiring a simultaneous insertion of the winding's several conductors into the stator core. Further, the resulting transitional (interleaved) end loop segments, which extend either radially-inwardly and/or radially-outwardly of the end loops segments interconnecting the straight segments of the cascaded layer, with such interleaved end loop transitions either protruding more than one conductor width into the internal diameter of the stator core, or extending radially outwardly of a given stator core slot more than one conductor width, thereby undesirably increasing stator package size.
Accordingly, what is needed is a method for making a stator assembly for a dynamoelectric machine, and preferably a method of prefabricating a stator winding preform for insertion into to a stator core to obtain such a stator assembly, featuring a cascaded winding whose interleaved conductor transitions do not position any conductor more than one conductor width radially-outwardly of the radially-outermost conductor layer.